Passenger vehicles often include electric batteries for operating features of a vehicle's electrical and drivetrain systems. For example, vehicles commonly include a 12V lead-acid automotive battery configured to supply electric energy to vehicle starter systems (e.g., a starter motor), lighting systems, and/or ignition systems. In electric, fuel cell (“FC”), and/or hybrid vehicles, a high voltage (“HV”) battery system may be used to power electric drivetrain components of the vehicle (e.g., electric drive motors and the like).
In certain designs, battery systems included in a vehicle may include one or more sections. For example, a vehicle battery system may include a battery pack that comprises one or more sections of battery cells, such as many current battery systems for electric vehicles, including rechargeable energy storage systems (RESS) for extended-range electric vehicles (EREV). Battery sections may be replaced and/or added in a battery pack, resulting in differences in capacities, state of charge, discharge rates, impedances, and/or voltages between the new battery sections and the existing battery sections. Battery discharge may terminate when a section having the lowest capacity is depleted, regardless of whether other battery sections have sufficient capacity for sustained discharge. This behavior may result in battery system inefficiencies, degradation, and/or permanent damage.
Typically used sections are not replaced without a section balancing strategy. Such strategies are particularly important for dealing with energy storage chemistries that must maintain certain voltage limits for safety reasons, such as Lithium Ion batteries. Current cell balancing methods coupled with section replacements can cause unnecessary taxation on a rechargeable electricity storage system. Existing section balancing methods, however, tend to allow for too much spread between sections due to varying section states of health. Moreover, many such methods are not operational to minimize state of charge spread throughout the charge/discharge cycle of the system. Instead, existing section balance methodologies tend to balance based on the state of charge spread at key-on.
The present inventors have therefore determined that it would be desirable to provide methods and systems for balancing battery sections that overcome one or more of the foregoing limitations and/or other limitations of prior art.